The present invention relates, in general, to rotary clamps for linear actuators, and, more particularly, to a rotary clamp having a linkage assembly that provides an over-center condition for providing high actuation and clamping forces without excessively wearing the components of the linkage assembly.
Rotary clamps are known of the type in which linear actuator reciprocating movement is adapted to be translated into angular rotary movement of a clamp arm. The linear actuator may be powered by a fluid motor, and an additional linkage or other transmitting means converts the linear actuator motion into rotary clamp motion. Normally, when the fluid motor is in a retracted position, the clamp is in a released position, that is, the clamp arm is removed from the work supporting surface. When the fluid motor is an extended position, the clamp arm is pivotally moved into a clamping position to clamp a workpiece to a work supporting surface and hold and/or locate the workpiece against the work supporting surface.
Various guide and linkage means have been proposed to correctly translate linear reciprocating movement of a piston and piston rod, utilized in the linear actuator, to correctly swing the clamp arm into or out of clamping position and obtain the highest mechanical advantage which can be utilized within the power stroke of the linear actuator. All of these known mechanisms, more or less, include complex designs of various mechanical components at high manufacturing and assembly costs.
A known design powers a linear actuator along a guide slot provided in a housing of the clamp. The linear actuator is pivotally connected to a linkage assembly which in turn is pivotally connected to a lever arm of a shaft link. The linear actuator provides reciprocal linear movement along the guide slot, thus driving the linkage assembly which converts the linear movement of the linear actuator into rotational movement of the shaft link. A clamp arm is connected to the shaft link wherein the shaft link provides rotary motion to the clamp arm between a clamped position and an unclamped position.
Typically, such designs try to prevent the overtravel of the linkage member to an over-center position wherein the pivot points of the linkage member are at a 0xc2x0 angle with respect to one another, in other words, the longitudinal axis of the linkage member is at a position perpendicular to the longitudinal axis of the guide slot. As the linkage angle approaches 0xc2x0, the linkage force approaches infinity through the relationship P=F÷(tangent xcex1) where P equals the linkage force, F equals the linear actuator force, and xcex1 equals the linkage angle. As the linkage member approaches the over-center position, the clamp mechanism experiences ultra high linkage forces which may cause premature wearing of the linkage mechanism or may cause the linkage mechanism to xe2x80x9cfreezexe2x80x9d or xe2x80x9clock upxe2x80x9d.
Other designs provide for the linkage mechanism to travel to a positive center or slight over-center locking position wherein needle bearings are utilized so that the cylinder pressure required to release the clamp is no greater than the cylinder pressure needed to actuate the clamp to the locking position. Such configurations are capable of producing high clamping forces, but they are also subject to undesirable wear to the internal mechanism created during the passage through the ultra-high force over-center position. The result of the wear is the reduction of the clamp forces in which the clamp can produce.
Thus, it would be desirable to provide a rotary clamp that provided a linkage member that could travel to an over-center position without experiencing the excessive wear that is common of rotary clamps which utilize over-center linkage members.
The present invention overcomes the above-noted shortcomings by providing a rotary clamp that provides for an over-center linkage position without experiencing excessive wear to the rotary clamp. The rotary clamp of the present invention provides a means for converting linear actuator motion between a first position and a second position into rotary clamp motion between an unclamped position and a clamped position, respectively. The present invention also provides a means for preventing a first link of the converting means from reaching an over-center position and allowing a second link of the converting means to reach an over-center position in the clamped position thereby creating higher clamping and actuating forces without causing wear to the clamp. A means for resisting movement of the converting means from said clamped position toward said unclamped position is also provided.
The converting means provides a linkage assembly connected to a linear actuator and a clamp arm. The linkage assembly includes a first link pivotally connected to a second link, and a third link pivotally connected to the second link.
The preventing means provides a pin received by an aperture provided in the first link of the linkage assembly wherein a roller is coaxially connected to the pin. The roller engages the third link of the linkage assembly when moving in and out of the clamped position, and the pin engages a wear surface in response to the roller engaging the third link to prohibit the first link from reaching the over-center position.
The resisting means provides a spring detent for engaging the roller and resisting movement of the rotary clamp from the clamped position to the unclamped position.